I've been using "Shiny" theme for months. It is a theme provided in Gmail theme settings, which has glossy Web 2.0 style design in every corner of it. But then I want to see something different, because I always checking my Gmail everytime I'm online, I thought it would be a great idea to create my own Gmail theme in simplified look. I wanted to have custom Gmail theme that has similar color schemes as my Twitter background. A Dark grey-scale theme with soft green color in some parts.
Wanna try to create something like mine? I'm using the web-safe default color schemes, so all you need is do the same thing as I did on your Gmail theme setting dashboard and save it. If you don't know how to create your own Gmail theme, just read this Gmail Help answer page for a start ;)